ATP receptors are basically classified into P2X family of ion-channel type receptors and P2Y family of G protein-coupled receptors. Until now, there are reported, respectively, seven sub-types (P2X1-7) and eight sub-types (P2Y1, 2, 4, 6, 11-14).
It has been reported that P2X4 receptor (Genebank No. X87763), which is a sub-type of P2X family, is present widely in the central nervous systems (cf. Non-patent documents 1-5).
The mechanism of pathogenesis of intractable pains such as neuropathic pain is unclear. Therefore, if non-steroidal anti-inflammatory drugs (NSAIDs) and morphine are not effective, there is no other pharmacotherapy. In that case, the patient and surrounding people take up a heavy burden in mind and body. The neuropathic pain is caused by injury of peripheral or central nervous systems, for instance, post-surgery pain, cancer, spinal cord injury, herpes zoster, diabetic neuritis, or trigeminal neuralgia.
Recently, Inoue, et al. studied the involvement of P2X receptors in neuropathic pain using dorsal root ganglion neuron-injured animal model, which induces allodynia, and indicated that the nerve-injured pain (particularly, allodynia) is caused via P2X4 receptors on spinal microglia (cf. Non-patent documents 6, 7, and Patent document 1).
Accordingly, compounds that inhibit the action of P2X4 receptors are expected to be employed for preventing or treating nociceptive, inflammatory, and neuropathic pains.
Patent document 2 discloses that benzofuro-1,4-diazepin-2-one derivatives having the below-illustrated formula (A) show P2X4 receptor antagonism:
wherein R1 is halogen, and R2 is hydrogen, halogen, nitro, cyano, C(O)—OR3, C(O)—NR4R5, SO2—R3, or SO2—NR4R5, or in which R1 is hydrogen, and R2 is halogen, nitro, cyano, C(O)—OR3, C(O)—NR4R5, SO2—OR3, or SO2—NR4R5.
Non-patent document 8 discloses that Paroxetine known as an antidepressant also shows P2X4 receptor antagonism.
The present inventors have found that naphtho[1,2-e]-1,4-diazepin-2-one derivatives having the below-illustrated formula (B) showing P2X4 receptor antagonism, and filed the Patent document 3.

Patent document 4 discloses a naphtho[1,2-b]-1,4-diazepin-4-one derivative represented by the following formula (C).

Patent document 4 describes that the compound represented by the formula (C) can be used as photographic couplers. Patent document 4, however, is silent with respect to the relation between the compound and the P2X4 receptor antagonism.
Patent document 5 describes the quinoxaline compound represented by the formula (D).

In the formula (D), R1 can be an aryl group, and R5 and R6 can be combined together to form an aromatic ring. Patent document 5, however, is silent with respect to an example of a quinoxaline compound wherein R1 is an aryl group. Patent document 5 describes that the quinoxaline compound represented by the formula (D) has a quisqualate receptor antagonism. Patent document 5, however, is silent with respect to the relation between the compound and the P2X4 receptor antagonism.